[Lucid 1/2 SRU] xen: just completely disable XSAVE

[Stefan Bader]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge at citrix.com>

Some (old) versions of Xen just kill the domain if it tries to set any
unknown bits in CR4, so we can't reliably probe for OSXSAVE in
CR4.

Since Xen doesn't support XSAVE for guests at the moment, and no such
support is being worked on, there's no downside in just unconditionally
masking XSAVE support.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>

BugLink: http://bugs.launchpad.net/bugs/1044550

(cherry-picked from commit 61f4237d5b005767a76f4f3694e68e6f78f392d9 upstream)
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 arch/x86/xen/enlighten.c |   18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8e72dd..e66c9ce 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -224,23 +224,7 @@ static __init void xen_init_cpuid_mask(void)
 			~((1 << X86_FEATURE_APIC) |  /* disable local APIC */
 			  (1 << X86_FEATURE_ACPI));  /* disable ACPI */
 
-	ax = 1;
-	cx = 0;
-	xen_cpuid(&ax, &bx, &cx, &dx);
-
-	/* cpuid claims we support xsave; try enabling it to see what happens */
-	if (cx & (1 << (X86_FEATURE_XSAVE % 32))) {
-		unsigned long cr4;
-
-		set_in_cr4(X86_CR4_OSXSAVE);
-		
-		cr4 = read_cr4();
-
-		if ((cr4 & X86_CR4_OSXSAVE) == 0)
-			cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_XSAVE % 32));
-
-		clear_in_cr4(X86_CR4_OSXSAVE);
-	}
+	cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_XSAVE % 32)); /* disable XSAVE */
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
-- 
1.7.9.5